476 HISTORY OF PHYSICAL ASTRONOMY. 



Such telescopes might be expected to add something- to our knowl- 

 edge of the heavens, if they had not been anticipated by reflectors o! 

 an equal or greater scale. James Gregory had invented, and Newton 

 had more efficaciously introduced, reflecting telescopes. But these 

 were not used with any peculiar effect, till the elder Herschel made 

 them his especial study. His skill and perseverance in grinding 

 specula, and in. contriving the best apparatus for their use, were re- 

 warded by a number of curious and striking discoveries, among which, 

 as we have already related, was the discovery of a new planet beyond 

 Saturn. lu 1789, Herschel surpassed all his former attempts, by 

 bringing into action a reflecting telescope of forty feet length, with a 

 speculum of four feet in diameter. The first application of this mag- 

 nificent instrument showed a new satellite (the sixth) of Saturn. He 

 and his son have, with reflectors of twenty feet, made a complete 

 survey of the heavens, so far as they are visible in this country ; and 

 the latter is now in a distant region completing this survey, by adding 

 to it the other hemisphere. 



In speaking of the improvements of telescopes we ought to notice, 

 that they have been pursued in the eye-glasses as well as in the ob- 

 ject-glasses. Instead of the single lens, Huyghens substituted an eye- 

 piece of two lenses, which, though introduced for another purpose, 

 attained the object of destroying color. 6 tlamsden's eye-piece is one 

 fit to be used with a micrometer, and others of more complex construc- 

 tion have been used for various purposes. 



Sect. 2. Observatories. 



ASTRONOMY, which is thus benefited by the erection of large and 

 stable instruments, requires also the establishment of permanent Ob- 

 servatories, supplied with funds for their support, and for that of the 

 observers. Such observatories have existed at all periods of the his- 

 tory of the science ; but from the commencement of the period which 

 we are now reviewing, they multiplied to such an extent that we can- 

 not even enumerate them. Yet we must undoubtedly look upon such 

 establishments, and the labors of which they have been the scene, as 

 important and essential parts of the history of the progress of astron- 

 omy. Some of the most distinguished of the observatories of modern 



/ O 



times we may mention. The first of these were that of Tycho Brahe 



CoJilington's Optics, ii. 21. 



